Warning: array_merge() after setting access

Hi,
I’ve installed the UAM plugin and it worked, but after setting access privileges to categories and posts I have this error in the home.

Warning: array_merge() [function.array-merge]: Argument #1 is not an array in /home/santama/public_html/honduras/wp-content/plugins/user-access-manager/class/UserAccessManager.class.php on line 1425

The error does not prevent the home to be displayed, and the access permisions are working. What is that warning message and how can I get rid of it?

Thank you!!!
L.